The present invention relates to the art of digital data communications and, more particularly, to apparatus and method of converting digital data received at one bit rate and then outputting the data at a different bit rate.
The present invention has particular application wherein data is obtained at rates which are greater than that which can be received in real time by state-of-the-art computers. For example, the present state-of-the-art computers can read or receive data at rates of upwards of 1 million bits per second, but not at data rates on the order of, for example, 20 million bits per second. Image processing systems, for example, use satellites and may generate data at very high data rates, such as 20 million bits per second, and this data cannot be processed in real time by a computer.
It is desirable in such a system to record the data on a suitable recording medium, such as typical magnetic recording tape. This may be done at essentially the same speed as the data is being received. Later, the data may be read out at a transport speed which permits a lower bit rate. Also, it is desirable in such a system that the data be divided from the single channel, as received, into multiple channels and recorded on a multiple channel recording medium. During the read-out process, the data is read from the multiple channels and should be rearranged in the same sequence in which received and then outputted at a desired bit rate for processing by a computer or the like.
In addition to the foregoing, it is also desirable to increase the bit packing density in order to maximize the number of bits recorded per inch on magnetic tape. This may be accomplished by known recording schemes. However, a notable disadvantage in high density bit packing is that bit skew becomes of considerable concern. Skew is defined as the time displacement between two reproduced data bits that were recorded simultaneously on different tracks.
It is also desirable in such a system that during the readout process, circuitry be employed for deriving or reconstructing a clock signal from the bits recorded in an associated recording track. However, if there is a degradation in the signal level of the bits recorded in that track, then this will adversely affect the reconstructed clock rate.